Self administered injectable medicaments are often delivered using a variable-dose injection device. Such a device is known from WO 2004/078239 A1. Prior to the injection the user selects the dose that they require according to their prescribed dose and/or their current or expected future physical condition. A typical example would be an insulin delivery device for diabetics where a patient's dose is determined according to their prescribed dose and their expected food intake and activity level. Typically such devices allow the user to select any dose from 1 unit up to the maximum unit dose that the device can deliver, typically 60 units or 80 units for a manual device, such as a pen-type or syringe injection device.
Pen type drug delivery devices have been designed and developed to perform regular injections by persons without formal medical training. This is increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. Because the patient, and not the health care worker, may be using such a drug delivery device, one requirement is that the device should be robust in construction. The drug delivery device must also be easy to use both in terms of the drug delivery device manipulation and understanding of the device's operation. This is especially true for diabetics who are required to inject themselves repeatedly with insulin solution and the volume of insulin to be injected may vary from patient to patient and even from injection to injection. For at least this reason, certain diabetics may require drug delivery devices that allow the patient to inject successive measured dosages of the same or perhaps different preset volumes of insulin solution accurately and with minimum dexterity challenges. This presents a further design challenge since, in the case of certain diabetics, users may have impaired vision and/or may be physically infirm with limited dexterity.
In addition to insulin, other medicaments require a minimum dose to be delivered before they are therapeutically effective. A variable-dose device that allows the patient to deliver doses below the therapeutically effective minimum dose creates the possibility that the user may deliver the ineffective doses either by an error of dose calculation or by mistakenly selecting the incorrect dose. Likewise, some medicaments require that a maximum dose is not to be exceeded. This may be for safety reasons such as increased risk or severity of side-effects or excessive or unwanted actions of the medicament. Current variable-dose delivery devices typically have a maximum dose that is limited by the maximum dose that the delivery mechanism can provide, however, this does not necessarily relate to the maximum advised or prescribed dose of the medicament.
From WO 02/064199 A1 with a device for administration of an adjustable dose of an injectable product with an adjustment lock for the set dose is known that prevents inadvertent change of the set dosage. While being connected to a housing, dosing and actuating means perform the functions of the dose setting and the operation of a conveyor. In order to lock the dose set, a plug-in body is attached to the injection device's body, said body comprising a first and second plug-in body portion. The first plug-in body portion axially fixes the plug-in body to the injection device, while the second performs the function of shielding the dosing element against adjusting movements by the user, thereby preventing unintended change of the set dose.
EP 2 351 591 A1 is directed at a device with an end-stop mechanism that prevents dialing once a final dose is reached, said mechanism including a stop feature located at a rotation member, a drive member rotationally coupled to a piston rod by means of a longitudinal guide rib/notch-connection and further coupled to the rotation member by means of a uni-directional clutch mechanism. The piston rod comprises a blocking member interacting with the stop feature on the rotation member. With each injection process, blocking member and stop feature advance towards each other. Once blocking member and stop feature abut, rotation of the stop feature and the rotation member is prevented.